The present invention relates generally to bar code reading devices, and more particularly, staring collection optics for flying spot type barcode readers.
In recent years, businesses in many industries including retail, manufacturing, transportation, and warehousing have encoded identification data into barcodes to facilitate identification and tracking of products in commerce.
Typically, an alphanumeric code identifying a particular product or container of products will be encoded into barcode symbol consisting of a plurality of contrasting parallel bars and spaces of varying widths. Barcode readers have been designed to read the barcode symbol and make the encoded identification data available to a computer system to which the barcode reader is connected.
One typical barcode reader architecture, commonly called a laser scanner, includes a laser illumination source providing a laser beam and an optic system for focusing the laser beam to a very narrow waist such that it provides a pin point spot of illumination on an object in the path of the beam. The laser beam is reflected from an oscillating or spinning scanning mirror which sweeps the beam and thus causes the spot of illumination to xe2x80x9cflyxe2x80x9d across a reading axis of the barcode. The parallel bars and spaces typically define a vertical axis and the read axis is generally perpendicular to the parallel bars and spaces such that it crosses all bars and spaces and generally defines a horizontal axis. As the spot of illumination flies across the parallel bars and spaces, the dark bars generally absorb the illumination while the light colored spaces generally reflect the illumination such that modulated reflected illumination is reflected from the code during the time period while the spot flies across the parallel bars and spaces. The modulation is a function of the spot speed, spot size, and the width of each bar and space.
A staring photodetector, which has a field of view that encompasses the read axis of the barcode, detects the modulated reflected illumination and generates a modulated electrical signal corresponding to the modulated reflected illumination. Signal processing and decoding circuitry operate to decode the electrical signal from the photodetector and provide the alphanumeric data to a computer system coupled thereto. While a laser scanner using a scanning mirror is the most common architecture for generating a flying spot for reading a barcode, alternatives include moving the entire laser illumination source to generate a flying spot across the reading axis of the barcode.
A problem associated with flying spot type barcode readers is that the photodetector, in addition to detecting the modulated reflected illumination, also detects ambient illumination which degrades the signal to noise ratio of the electrical signal and degrades the performance of the reader.
To improve signal to noise ratio, optics can be used to limit the field of view of the staring photodetector to a narrow rectangular region surrounding the reading axis of the code to reduce the amount of ambient illumination from regions above and below the read axis that is detectable by the photodetector. An example of such a limited field of view system 8 is shown in FIGS. 1(a) and 1(b). Photodetector 10 includes a plurality of photodetectors 10(a)-(d) and is positioned behind an optic 12. Referring to FIG. 1(a) which is a top view of the system 8, optic 12 functions to gather illumination from a wide horizontal field of view 14 which entirely encompasses read axis 16 through code 18. Referring to FIG. 1(b), which is a side view of the system 8, optic 12 functions to gather illumination from a narrow vertical field of view 20, again encompassing the entire read axis 16, but not encompassing regions 22(a) and 22(b) above and below the code 18. As such, ambient illumination from regions 22(a) and 22(b) does not contribute to ambient illumination noise on the photodetector 10. In known solutions, the optic surface 24 of optic 12 is toroidal and is large enough so that photodetector 10 defines the optical aperture of the system 8 (e.g. how much of the light reflected from the laser beam spot can be gathered and reflected onto the photodetector). A problem associated with existing rectangular field of view systems is that because the optic is large enough for the photodetector to define the optical aperture, the size and weight of the optic hinder the design of extremely compact barcode reading solutions for portable applications.
Another solution to improve signal to noise ratio is a retro-reflective architecture. In a retro-reflective device, mirrors and/or lenses are used to limit the field of view of the photodetector to an area significantly smaller than the entire read axis of the barcode. An oscillating or spinning collection mirror than sweeps the field of view of the photodetector in unison with the flying spot to detect the reflected illumination. The oscillating or spinning collection mirror typically defines the optical aperture of the system and therefore must be large enough to gather enough light to provide for an improved signal to noise ratio over a staring system. Problems associated with retro-reflective systems are size, cost, complexity, and power consumption associated with a system in which a large collection mirror spins or oscillates.
What is needed is a flying spot barcode reading system that provides for a strong signal to noise ratio but does not suffer the disadvantages of size, cost, complexity, and power consumption of known retro-reflective barcode scanner and does not suffer the disadvantages of size and weight associated with known limited field of view staring systems.
A first object of this invention is to provide a code scanner comprising a flying spot illumination source sweeping an intense spot of illumination across a scan axis of a code to generate a modulated reflected illumination and a photodetector assembly for receiving the modulated reflected illumination from a code. The photodetector includes: i) a photosensor; ii) a lenticular array positioned between the photosensor and the code and including a plurality of lens elements for refracting illumination, including the modulated reflected illumination and ambient illumination; and iii) a mask positioned between the photosensor and the lenticular array blocking at least a portion of the ambient illumination from impinging on the photosensor.
In a first embodiment, the plurality of lens elements are horizontal lens elements arranged in a vertical array and the mask includes a plurality of horizontal mask elements, the horizontal mask elements being interlaced between the plurality of horizontal lens elements. The plurality of horizontal lens elements may be on a front surface of the lenticular array facing the code.
The plurality of horizontal mask elements define a plurality of horizontal spaces in alignment with the plurality of horizontal lens elements and defining a vertical field of view from which illumination originating in the vertical field of view is generally refracted towards a horizontal space and illumination originating outside of the vertical field of view is generally refracted towards a horizontal mask element. Each lens element has a curvature defining a focal point, the focal point may be positioned behind the mask.
In one sub embodiment, the mask is an illumination absorbing coating on a back surface of the lenticular array. In a second sub embodiment, the mask is a planar material including the plurality of horizontal spaces positioned therein and the mask is spaced apart from the back surface of the lenticular array. In a third sub embodiment, the lenticular array is a molded optic material and the photosensor and mask are embedded therein.
In a second embodiment, the plurality of lens elements are arranged in a two dimensional array and the mask defines a plurality of horizontal space regions each bounded a light blocking region, each space region defining a vertical field of view from which illumination originating in the vertical field of view is generally refracted towards a horizontal space region and illumination originating outside of the vertical field of view is generally refracted towards the light blocking region. The plurality of lens elements maybe on a front surface of the lenticular array facing the code and each horizontal space region may be positioned behind a lens element. Each lens element has a curvature defining a focal point, the focal point may be positioned behind the mask.
In one sub embodiment, the mask is an illumination absorbing coating on a back surface of the lenticular array. In a second sub embodiment, the mask is a planer material including the plurality of horizontal spaces positioned therein and the mask is spaced apart from the back surface of the lenticular array. In a third sub embodiment, the lenticular array is a molded optic material and the photosensor and mask are embedded therein.
A second objective of the present invention is to provide a photodetector assembly for detecting illumination from a field of view, comprising: a) a photosensor; b) a lenticular array positioned in front of the photosensor including an array of lens elements; and c) a mask positioned between the photosensor and the lenticular array blocking at least a portion of the illumination from impinging on the photosensor.
In a first embodiment, the plurality of lens elements are horizontal lens elements arranged in a vertical array and the mask includes a plurality of horizontal mask elements, the horizontal mask elements being interlaced between the plurality of horizontal lens elements. The plurality of horizontal lens elements are on a front surface of the lenticular array facing the code. The plurality of horizontal mask elements define a plurality of horizontal spaces in alignment with the plurality of horizontal lens elements and defining a vertical field of view from which illumination originating in the vertical field of view is generally refracted towards a horizontal space and illumination originating outside of the vertical field of view is generally refracted towards a horizontal mask element. Each lens element has a curvature defining a focal point, the focal point may be positioned behind the mask.
In one sub embodiment, the mask is an illumination absorbing coating on a back surface of the lenticular array. In a second sub embodiment, the mask is a planar material including the plurality of horizontal spaces positioned therein and the mask is spaced apart from the back surface of the lenticular array. In a third sub embodiment, the lenticular array is a molded optic material and the photosensor and mask are embedded therein.
In a second embodiment, the plurality of lens elements are arranged in a two dimensional array and the mask defines a plurality of horizontal space regions each bounded a light blocking region, each space region defining a vertical field of view from which illumination originating in the vertical field of view is generally refracted towards a horizontal space region and illumination originating outside of the vertical field of view is generally refracted towards the light blocking region. The plurality of lens elements may be on a front surface of the lenticular array facing the code and each horizontal space region may be positioned behind a lens element. Each lens element has a curvature defining a focal point, the focal point may be positioned behind the mask.
In one sub embodiment, the mask is an illumination absorbing coating on a back surface of the lenticular array. In a second sub embodiment, the mask is a planer material including the plurality of horizontal spaces positioned therein and the mask is spaced apart from the back surface of the lenticular array. In a third sub embodiment, the lenticular array is a molded optic material and the photosensor and mask are embedded therein.
A third objective of the present invention is to provide a lenticular array comprising a front surface including an array of horizontal lens elements and an opaque mask including an array of horizontal mask elements positioned behind the front surface, the array of horizontal mask elements being interlaced between the array of horizontal lens elements. Each lens element has a curvature defining a focal point, the focal point may be positioned behind the mask.
In one sub embodiment, the mask is an illumination absorbing coating on a back surface of the lenticular array. In a second sub embodiment, the mask is a planer material including the plurality of horizontal spaces positioned therein and the mask is spaced apart from the back surface of the lenticular array. In a third sub embodiment, the lenticular array is a molded optic material and the photosensor and mask are embedded therein.
A fourth objective of the present invention is to provide a method of reading a code comprising: a) illuminating the code with a point of illumination sweeping across a sweep axis of the code to generate modulated reflected illumination; b) refracting illumination from a field of view towards a photosensor with an array of a plurality of refractive lens elements, the field of view having a width encompassing the sweep axis and a height less than the width; and c) refracting illumination from a region above and a region below the field of view towards an illumination blocking mask. In one embodiment, the plurality of refractive lens elements are horizontal lens elements arranged in a vertical array and in a second embodiment the plurality of refractive lens elements are circular lens elements arranged in a two dimensional array.